Relief valve control mechanism for suction dredges

Claim 1

IN A SUCTION DREDGE HAVING A PUMP, A SUCTION PIPE LEADING TO THE PUMP, AND A NORMALLY CLOSED UNDERWATER RELIEF VALVE ON THE PIPE; MEANS TO CLOSE THE VALVE AND HOLD THE SAME CLOSED WHEN PUMPING CONDITIONS ARE NORMAL AND A NEGATIVE PRESSURE DIFFERENTIAL EXISTS ALONG THE SUCTION PIPE, AND MEANS TO OPEN THE VALVE RESPONSIVE TO CONDITIONS OF EQUALIZED PRESSURE EXISTING ALONG THE SUCTION PIPE AS OCCASIONED BY A STOPPAGE IN THE SUCTION PIPE AT THE WATER ENTRY END THEREOF; SAID LAST NAMED MEANS INCLUDING AN ELECTRICAL DEVICE WHICH WHEN ENERGIZED PREVENTS THE VALVE FROM BEING OPENED, A CIRCUIT IN WHICH THE DEVICE IS INTERPOSED AND HAVING A SWITCH INTERPOSED THEREIN, THE SWITCH INCLUDING A LEVER SWINGABLE IN ONE DIRECTION OR THE OTHER TO CLOSE OR OPEN THE SWITCH, A PAIR OF OPPOSED VACUUM CHAMBERS BETWEEN WHICH THE LEVER IS DISPOSED, SAID VACUUM CHAMBERS HAVING ADJACENT MOVABLE ENDS ENGAGING THE LEVER ON OPPOSITE SIDES THERREOF, AND A PAIR OF STANDPIPES MOUNTED ON THE SUCTION PIPE AT RELATIVELY WIDELY SPACED POINTS IN THE LENGTH THEREOF AND COMMUNICATING WITH SAID SUCTION PIPE AND WITH CORRESPONDING CHAMBERS; ONE STANDPIPE BEING LOCATED ADJACENT THE PUMP; THE LAST NAMED STANDPIPE BEING CONNECTED TO THAT ONE OF THE CHAMBERS WHICH WILL CAUSE THE MOVABLE END THEREOF TO BE DRAWN AWAY FROM THE LEVER SO THAT THE LATTER WILL BE MOVED IN SAID ONE DIRECTION TO A SWITCH CLOSING POSITION WHEN THE NEGATIVE PRESSURE IN SAID NEAREST STANDPIPE EXCEEDS THAT IN THE OTHER STANDPIPE, AND WILL BE MOVED IN SAID OTHER DIRECTION TO A SWITCH OPENING POSITION WHEN THE NEGATIVE PRESSURE IN BOTH STANDPIPE IS EQUALIZED.